1. Field of the Invention
The present invention generally relates to gun-launched projectiles, and in particular to a method for detecting a launch using a projectile borne continuous wave radio frequency signal in which the detection of the launch is used to arm a fuze in a gun-launched projectile.
2. Background of the Invention
Gun-launched projectiles utilize a safety and arming (S&A) device within a fuze to arm a projectile after launch. The projectile is considered armed when the fuze becomes armed after a valid gun launch is detected. The criterion for projectile fuze safety and arming is that a minimum of two independent launch environments or events must be confirmed before the projectile can be armed. Acceleration experienced by the projectile during launch (known as setback) and spin imparted to the projectile during launch are two environments detected and used for arming. Setback and spin exhibit robust and unique signatures that are easily detectable.
A conventional approach to detecting a valid gun launch utilizes mechanical inertial safety and arming devices. The mechanical inertial safety and arming devices are designed to observe and sense setback in excess of some pre-designed threshold as the first confirmation of gun launch. In projectiles in which spin is induced during launch, the mechanical inertial safety and arming devices are designed to observe and sense projectile spin in excess of some pre-designed threshold as the second confirmation of gun launch. However, fin-stabilized projectiles such as mortars and tank ammunition do not experience measurable spin during gun launch. Consequently, absence of spin stabilization requires the use of features of the launch environment other than spin to provide the necessary second safety signature for arming.
Conventional approaches for detecting the second safety signature have taken the form of detecting ram air pressure during flight, umbilical disconnect of an interface cable, or fin deployment once the projectile leaves the gun barrel. Although this technology has proven to be useful, it would be desirable to present additional improvements. The conventional approaches for detecting the second safety signature are difficult to implement on projectiles that do not or can not breathe air from the air stream during launch, use fixed-fin tail assemblies, or do not have an umbilical connection to a weapon platform. For projectiles that can breathe air from the air stream during launch, ports for diverting the air stream through the launch detector can become clogged, preventing operation of the second safety feature.
What is needed is a method for detecting a second safety signature of the launch of a projectile in conjunction with the detection of setback. This method for detecting the second safety signature should be applicable to projectiles such as those projectiles that do not breathe air from the air stream during launch, that use fixed-fin tail assemblies, that do not have an umbilical connection to a weapon platform, or that are not spin-stabilized. The need for such a system has heretofore remained unsatisfied.